new potato cultivars - university of...

Agronomics of New Potato Varieties - ADF Project 20100006

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Prepared by: Doug Waterer

Vegetable Crop Specialist, Dept. of Plant Sciences

University of Saskatchewan

Research Supported by:

Saskatchewan Agriculture and Food

Saskatchewan Seed Potato Growers Association

Background. These trials are designed to determine the optimum growing

practices for the new potato lines licensed to the Saskatchewan Seed Potato

Growers (SSPGA), along with any new lines from other breeding programs

that have been identified as being of particular interest to Saskatchewan’s

potato industry. Timely development of a package of appropriate

management practices is crucial to market success of new potato varieties.

The trials conducted in 2015 were designed to build on previous trials (2008-

2014). See http://veg.usask.ca/potato-agronomy-research for complete reports for previous trials.

Key performance factors examined in 2015 included responses to soil moisture availability, time of

planting and harvest, N fertility and plant populations.

Materials and Methods

Cultivars tested in 2015 included;

Yellow fleshed

Milva – high yielding, good tasting line - exclusive to a SSPGA member

Marilyn – relatively unknown fingerling type line - exclusive to a SSPGA member

Conquine – relatively unknown line - exclusive to a SSPGA member

Miss Andes - relatively unknown line - exclusive to a SSPGA member

Miss Mignonne - relatively unknown line - exclusive to a SSPGA member

Chopin – high yielding line - exclusive to a SSPGA member

Bintje – standard yellow flesh variety – very popular in Europe

Natasha - relatively unknown line - exclusive to a SSPGA member

Campina – relatively unknown line - exclusive to a SSPGA member

401-1 - relatively unknown line - exclusive to a SSPGA member

Russet type

Ludmilla – russet suited to processing out of cold storage - Exclusive to a SSPGA member

Clearwater – new processing russet gaining popularity in USA

Field Performance and Agronomic Requirements of

New Potato Cultivars

http://veg.usask.ca/potato-agronomy-research


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Red skinned

Modoc – good storage red - SSPGA member as exclusive agent

AC Peregrine Red – high yielding red but is scab sensitive. Exclusive to the SSPGA

CVXXXX – a new numbered line being tested by a SSPGA member

The new lines were evaluated in comparison with established industry standard lines;

Red standards : Norland, Sangre, Pontiac

Yellow standards : Yukon Gold

Russet standards : Russet Norkotah, Russet Burbank

Processing standards : Shepody, Kennebec

Planting * Harvest Trials

The objective of this trial was to evaluate how quickly each cultivar developed tubers/yields.

Trials were planted in either the mid-May (early planting) or early June (late planting). A

section of each planting date trial was harvested in late August (early harvest), with the

remainder of the plot being harvested in late September. This arrangement of planting and

harvest dates resulted in plants that were in the field for 80, 90, 105 and 120 days.

Dryland Trial As a significant portion of the North American potato crop is grown without the benefit of

irrigation, the objective of this trial was to evaluate the performance of the various new

cultivars under rainfed growing conditions. All lines were tested under dryland conditions

and yields were compared to irrigated production. This trial was planted in mid-May and

harvested in mid-September.

N Fertility trial

Sufficient N (46-0-0) was applied as a broadcast prior to planting to raise total soil N fertility

levels (residual + applied) to 50, 100, 150, 200 or 250 kg/ha. Application of 150-175#/a total

N is the standard recommendation for irrigated potatoes in Saskatchewan. While application

of higher rates of N may have a marginally positive impact on yields any gain comes at a

very high cost – both in terms of inputs and potentially negative effects of the environment.

Spacing trial

Each cultivar was tested at in-row spacings of 15, 23 or 35 cm. The 35 cm spacing is typical

of potatoes grown for maximum size (processing), or in situations where moisture may be

limited. The 15 cm spacing typically results in very high yields with a smaller average tuber

size. High yields of small tubers is desirable in the production of seed potatoes. The increase

in seed costs associated with close spacing needs to be considered relative to the anticipated

increase in yields.

Test Site Description

All trials were conducted on the Plant Sciences Department Potato Research plots located in

Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. The field was prepared

by first double disking. Unless otherwise specified, enough 46-0-0 was then broadcast to raise the

total N level in the field (residual + applied) to 150 kg N/ha. This N fertilizer was incorporated by


3 Fig. 2015-1. Soil water potentials, rainfall and potato field

irrigation in 2015

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Saskatoon - 2015

Dryland

Irrigated

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Saskatoon - 2015

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Irrigation

shallow tillage. Soil tests indicated that levels of all nutrients in the soil were adequate for potato

production. Each treatment plot consisted of a single, 8-m long section of row. Unless otherwise

specified, the row spacing was 1 m between rows with 23 cm between plants within a row. Weed

control was achieved by applying EPTC + metribuzin prior to planting, followed by linuron applied

at ground crack and rimsulfuron applied 3 weeks later. The crop was hilled twice prior to ground

crack and again 2 weeks later just as the plants were beginning to touch between rows. Unless

otherwise specified, the crop was overhead irrigated whenever soil water potentials averaged over the

effective root zone (0-30 cm) fell below -50 kPa. Foliar fungicides were applied as a means of

preventing outbreaks of disease such as early and late blight. Unless otherwise specified, the trials

were top-killed using diquat in early September (ca. 100 DAP) and machine harvested in late

September through early October. The crop was harvested with a Grimme harvester. Harvested

tubers were cured for 10 days at 15oC, graded and then cooled to 5oC for longterm storage. The

tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm

and oversize = > 88 mm diam. Marketable yields consisted of all physically sound and uniformly

shaped potatoes > 33 mm diam. Specific gravities were determined using the weight in air/weight in

water method of determination. A high specific gravity is indicative of processing potential,

whereas low specific gravities indicate either an immature potato or a potato suited only for table use.

The boiling, baking, chipping and frying quality of the various lines were evaluated using standard

methodologies.

2015 Project Results

2015 Growing Season The winter of 2014/2015 in Saskatoon was

long and cold which helped reduce

populations of Colorado Potato Beetles

below the action threshold. The 2015

Potato Agronomy trials were planted in the

2nd week of May 14 – which is a little

earlier than normal. Temperatures during

the 2015 growing season were about

normal, with record low amounts of rainfall

through late July. As a consequence of the

dry conditions, weekly irrigation

commenced soon after crop emergence in

mid-June and continued through until the

crop was desiccated in early September. A

total of 22 cm of water was applied over

nine irrigation events in 2015. Total rainfall

during the growing period amounted to 15

cm for a total of 37 cm of water received by

the 2015 crop.

Crop Health - Emergence was quick,

uniform and complete in most trials. The

combination of hilling and herbicides


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provided acceptable but not complete weed control. There were some escapes of red root pigweed

and green foxtail – however weed populations were not likely sufficient to impact yields. Some

mechanical damage occurred to a few rows during the 2nd hilling operation in several of the trials.

Some plants were knocked out of the hill and many others would have experienced significant root

damage. This damage may have reduced the yields in some of the plots. Data from the damaged

plots were not included in any analyses. No significant problems with foliar disease were observed

and the crop stayed healthy throughout the growing season.

Top kill, harvest and grading of the 2015 potato crop went as planned.

Yields in the 2015 trials were only average. This was surprising as the crop had been planted early,

growing conditions were generally good and the crop had appeared healthy throughout the growing

season.

The incidence and severity of common scab observed in the various trials was quite high – this was

surprising as this is only the second time in recent history that this land has been planted to potatoes.

The incidence and severity of the scab infestation was also quite variable across the plot area which

made it difficult to accurately evaluate the test cultivars’ susceptibility to this disease problem.

Results

Dryland Production Trials (2012-2015)

Dryland Trial in 2012 (for more details see the 2012 progress report)

Record rainfall levels minimized drought stress on the dryland potatoes through until late July of

2012. In August the combination of minimal rain and a large healthy crop canopy resulted in a quick

drawdown of soil moisture reserves.

Sangre was the highest yielding red-skinned potato in the 2012 dryland trial (Table 2015-1). This

was surprising – as in the irrigated trial yields of Sangre consistently lagged behind all other red-

skinned lines. Russet Norkotah was the highest yielding Russet–type potatoes under dryland

conditions. Russet Norkotah is an early maturing table type potato – and early maturity is helpful in

situations where soil moisture reserves become limited as the growing season progresses. Once

again cv. Milva was more productive than any of the other yellow fleshed cultivars in the dryland

trial.

The soil at the 2012 dryland test site was heavily infested with Common Scab (Streptomyces

scabies). As common scab also tends to thrive under the dry warm soil conditions that prevail in

non-irrigated fields this trial offered an opportunity to evaluate the relative sensitivity of the various

potato lines to this serious disease (Table 2015-1). None of the russet types showed any scab in the

2012 dryland trial, even with the heavy degree of infestation present at this test site. Of the red-

skinned cultivars Norland had the greatest scab tolerance, followed by the new cv. Modoc. Of the

yellow fleshed cultivars tested, Milva and Toscana were far more scab tolerant than the standard

Yukon Gold.


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Table 2015-1. Yields under dryland conditions, dryland yields as a % of irrigated yields and

scab intensity levels under dryland conditions in 2012.

Reds Yield (t/ha)

Dryland Yield (% of Irrigated)

Yield After Grade

Out to Scab (t/ha) Modoc 35.3 b 70 b 2.8 b Norland 37.6 ab 71 b 8.5 a

Peregrine 36.8 ab 63 b 0 b Sangre 39.0 a 91 a 0 b

Avg 37.2 74 3.4

Russets Yield

(t/ha) Dryland Yield

(% of Irrigated)

Yield After Grade

Out to Scab (t/ha)

Alpine 32.9 bc 67 b 32.9 bc Blazer 38.1 a 71 b 38.1 a Classic 27.3 d 58 c 27.3 d

Clearwater 28.6 d 68 b 28.6 d Russet Burbank 30.0 b 61 c 30.0 b Russet Norkotah 34.9 ab 84 a 34.9 ab

Avg 31.9 68 32.0

Yellows Yield (t/ha)


Yield After Grade

Out to Scab (t/ha)

Milva 45.6 a 75 a 45.6 a Yukon Gem 35.6 b 63 bc 6.4 c Yukon Gold 33.3 b 68 ab 0 c

Toscana 37.0 b 59 c 35.5 b Avg 37.9 66 21.9

For each skin colour type, values within columns followed by the same letter are not significantly different (P=0.05)

Tubers graded out if scab affects >5% of tuber surface area

Dryland Trial 2013

There was virtually no precipitation from late July onwards in 2013. As that time period coincided

with the period of canopy growth, tuber set and tuber sizing of the 2013 crop – it is not surprising

that yields in the 2013 dryland trial were low relative to the adjacent irrigated trial. By the time the

crop was ready for top killing in early September the soil in the dryland trial was very dry and the

plants of most cultivars had started to drop their lower leaves. By contrast all cultivars in the

irrigated trials were still green and healthy prior to top kill.



Reds Yield (t/ha)


Scab

Intensity Yields After Grade Out to Scab (t/ha)

AC Peregrine 31.9 a 61 a 52 a 1.6 a

Modoc 22.8 b 36 c 60 a 0 a Norland 33.8 a 54 b 34 b 2.4 a


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Avg 29.5 50 49 1.3 Russets Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yields After Grade

Out to Scab (t/ha)

Classic 16.0 c 35 b 0 b 16.0 b Clearwater 23.6 b 56 a 0 b 23.6 a

Russet Burbank 28.1 a 51 a 8 b 24.5 a Russet Norkotah 31.3 a 50 a 33 a 6.3 c

Avg 24.8 48 10 17.8

Yellows Yield (t/ha)


Scab


Aladdin 24.2 d 39 d 64 a 0 c Annabelle 26.3 d 45 cd 55 b 1.3 c

Chopin 33.5 bc 53 b 31 c 2.4 c Jewel 37.3 ab 51 bc 18 d 9.3 b Milva 42.7 a 62 a 11 de 32.0 a Rosara 30.0 c 54 b 54 b 0 c

Toscana 30.6 c 45 cd 27 c 3.7 c Yukon Gold 28.2 cd 51 bc 67 a 0 c Yellow Star 32.0 bc 52 bc 6 e 32.0 a

Avg 31.6 50 36 8.9 For each skin colour type, values within columns followed by the same letter are not significantly different (P=0.05)

Scab intensity is the % of tuber surface area affected by scab

Tubers graded out if >5% of the tuber surface area is affected by scab

For the second year running Modoc proved to be more sensitive to drought stress than the other red-

skinned cultivars tested. The standard russet varieties (Burbank and Norkotah) proved to be more

tolerant of drought than the new introductions (Clearwater or Classic). Once again cv. Milva was

more productive than any of the other yellow fleshed cultivars in the dryland trial. The new cv.

Aladdin did very poorly under dryland conditions – but proved exceptionally productive if irrigated.

Scab was more severe in 2013 than in 2012 – likely because of the hotter, drier conditions that

prevailed through July and August of 2013. The new russet cultivars Classic and Clearwater showed

more scab tolerance than the standard Burbank or Norkotah cultivars in the 2013 dryland trial. Of

the red-skinned cultivars test Norland had the greatest scab tolerance but under the extreme scab

pressure present at this site grade out to scab in the Norland crop was still near 100%. Of the yellow

fleshed cultivars tested, Milva and Yellow Star showed outstanding scab tolerance. Yukon Gold,

which is presently the standard yellow fleshed cultivar grown in Saskatchewan, showed the greatest

sensitivity to scab of any of the cultivars tested in this project.

Dryland Trial 2014

The drought stress experienced in 2014 was less severe than in previous years – this could be

attributed to the combined effects of; a) June of 2014 had double the average precipitation and below average temperatures


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b) July of 2014 showed above average precipitation and below average temperatures

c) Temperatures in August and September were cooler than normal

Severe drought (SWP <-100kPa) in 2014 was limited to just 7 days in mid-August. By contrast in

2013, soil water potentials below-100kPa were recorded from early August through the remainder of

the growing season.



Reds Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yields After Grade

Out to Scab (t/ha)

AC Peregrine 44.1 a 79 a 66 a 0 b

Modoc 29.2 b 56 b 26 b 11.7 a

Norland 38.9 a 69 b 22 b 15.7 a

Avg 37.4 71 38 9.3

Russets Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yields After Grade

Out to Scab (t/ha)

Ludmilla 37.1 a 67 b 0 b 37.1 a

Shepody 37.0 a 83 a 82 a 0 d

Goldrush 28.8 b 70 b 0 b 28.8 b

Kennebec 34.8 a 58 c - -

Russet Burbank 35.4 a 67 b 3 b 35.4 a

Russet Norkotah 33.1 a 62 c 12 b 23.8 c

Avg 34.3 68 16 20.9

Yellows Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yields After Grade

Out to Scab (t/ha)

Belvedere 36.9 b 60 b 40 b 0.7 d

Chopin 46.6 a 80 a 59 a 0 d

Juwel 38.2 b 66 b 22 c 15.3 c

Milva 49.8 a 78 a 6 d 48.8 a

Toscana 44.9 a 76 a 27 c 20.2 bc

Yukon Gold 36.7 b 74 a 52 a 0.7 d

Yellow Star 31.6 c 62 b 10 d 26.5 b




Overall yields and yields as a % of irrigated in the 2014 dryland trial were considerably higher than in

2013 and roughly comparable to 2012. These yield differences correspond with the severity of the

drought stress encountered in the various test years.

For the 3rd year running Modoc proved to be more sensitive to drought stress than the other red-

skinned cultivars tested. All the russet varieties tested produced similar yields in the 2014 dryland

trial – except for Goldrush in which the yields lagged well behind all of the other lines. Goldrush

also performed poorly in the irrigated trials – which suggests that there may have been a problem


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with the quality of seed used in 2014. The data suggests that cv. Shepody is quite drought tolerant –

but these results are skewed by the fact that a significant portion of the Shepody crop in the irrigated

trial was graded out due to Late blight. As was seen in previous trials, Milva was more productive

than any of the other yellow fleshed cultivars under dryland conditions.

Scab levels in the 2014 dryland trial were less severe than in 2013 but more severe than in 2012.

Scab was more severe in 2013 because it stayed hot and dry from July onwards in that year. By

contrast, temperatures and rainfall in July and August of 2014 were more moderate. As was seen in

previous trials, Norland was the least scab sensitive of the red-skinned cultivars tested. Scab

sensitivity of Modoc appeared comparable to Norland in the 2014 trial – whereas in all previous

trials it had appeared to be much more sensitive to scab – showing little difference in sensitivity

relative to the extensively damaged AC Peregrine. Yields after grade out to scab were comparable

for Modoc and Norland in the 2014 trial.

Grade out due to excessive scab was much less common in the thick skinned russet varieties relative

to the thinner skinned red or yellow varieties. The new russet cultivar Ludmilla had an extremely

thick skin – rendering it completely immune to scab. By contrast, the skin of Shepody is quite thin

and it showed a very high rate of grade out to scab in 2014.

Of the yellow fleshed cultivars tested, Milva and Yellow Star once again showed outstanding scab

tolerance. As was seen in previous trials, Yukon Gold, which is presently the standard yellow

fleshed cultivar grown in Saskatchewan, proved to be very sensitive to scab – it produced almost no

marketable tubers when grown under conditions conducive to scab.

Dryland Trial 2015

The drought stress experienced in 2015 was different than in previous years. In past years, there has

been abundant rainfall early in the season and the crop only began to encounter drought stress in

August. By contrast in 2015 there was no rainfall until mid-July – and as a consequence the early

stages of crop development occurred under moderate to severe drought conditions (see Fig. 2015-4).

However, from mid-July onwards rainfall was sufficient to maintain near-adequate soil moisture

levels.



Reds Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yields After Grade

Out to Scab (t/ha)

AC Peregrine 30.6a 59a 62a 0

Modoc 29.1a 53a 41ab 1.5

CVXXXX 30.8a 57a 55a 0

Norland 27.4a 54a 26b 5.5

Pontiac 35.1a 55a 65a 0

Sangre 19.8b 39b 29b 1.0

Avg 28.8 53 46 1.3


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Russets Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yield After Grade

Out to Scab (t/ha)

Ludmilla 33.7a 66ab 0c 33.7a

Clearwater 25.7c 48c 4c 25.7a

Goldrush 34.7ab 68ab 0c 34.7a

Kennebec 39.2a 65ab 54a 0b

Russet Burbank 29.7bc 61bc 0c 29.7a

Russet Norkotah 35.7ab 78a 13bc 20.7a

Shepody 34.4ab 71ab 26b 5.2b

Avg 33.6 64 14 21.4

Yellows Yield

(t/ha)

Dryland Yield

(% of Irrigated)

Scab

Intensity

Yield After Grade

Out to Scab (t/ha)

Bintje 20.4b 37ef 49ab 0b

Campina 20.0b 37ef 24cd 2.0b

Chopin 34.8a 60bc 38bc 1.8b

Coquine 14.4c 27f 8e 13.7a

Marilyn 34.2a 56cd 19de 15.6a

Milva 25.9b 43de 18de 10.4a

Miss Andes 38.0a 51cde 60a 0b

Miss Mignonne 19.3bc 34ef 31cd 3.4b

Natasha 38.6a 83a 21de 17.3a

Yukon Gold 19.3bc 45cd 29cd 1.9b

401-1 33.2a 74ab 39bc 0b




Overall yields and yields as a % of irrigated in the 2015 dryland trial were lower than in 2014 and 2012

and comparable to 2013. These yield differences correspond with the severity of the drought stress

encountered in the various test years.

Sangre was the most drought sensitive of the red-skinned cultivars tested in 2015. This was an

interesting observation – as in the 2012 trial Sangre had performed exceptionally well under dryland

conditions. Overall the russet varieties appeared to be more tolerant of drought stress than the red or

yellow type potatoes. The new russet cultivar Clearwater did not perform well under drought stress.

Natasha, Chopin, Marilyn, 401-1and Miss Andes were the highest yielding yellow skinned cultivars

in the 2015 dryland trial. Yields of Natasha and 401-1 were closer to those obtained under irrigated

conditions than any of the other yellow fleshed cultivars tested. Coquine did not yield well under

dryland conditions. Milva which has produced outstanding yields in previous dryland trials did not

do well in the 2015 trial –perhaps because of the unusual timing of the drought stress in the 2015.

Scab levels in the 2015 dryland trial were comparable to previous years. Grade out to scab was

extremely high in all of the red-skinned cultivars tested under dryland conditions in 2015. As was

seen in previous trials, the standard cultivar Norland was the most scab resistant of the red-skinned

cultivars tested. Grade out due to excessive scab was much less common in the thicker skinned

russet varieties relative to the thinner skinned red or yellow varieties. The new russet cultivars


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Ludmilla and Clearwater had extremely thick skin – rendering them completely immune to scab.

Scab reduced marketable yields to near zero for many of the yellow fleshed cultivars tested under

dryland conditions (Miss Andes, Miss Mignonne, Campina, Chopin and 401-1). Coquine, Natasha,

Marilyn and Milva showed good levels of scab tolerance. As was seen in previous trials, Yukon

Gold, which is presently the standard yellow fleshed cultivar grown in Saskatchewan, proved to be

sensitive to scab – it produced almost no marketable tubers when grown under dryland conditions

conducive to scab.

Overall Summary of Dryland Production Trials (2012-2015)

Yields and quality of potatoes are sensitive to damage by drought stress. The studies conducted in this

project showed that the extent of the damage that could be expected depended on the cultivar of potatoes

being grown, as well as the severity and timing of the drought stress. This project identified red skinned

cultivars (AC Peregrine Red) and yellow fleshed cultivars (Milva) that were better able to tolerate drought

than the cultivars presently favored by the industry, but did not identify a russet type that was better than

the industry standard (Russet Norkotah). The project also demonstrated that problems with grade out to

scab disease can further reduce marketable yields under dryland conditions – but that in the yellow

fleshed category there were drought resistant cultivars like Milva, Yellow Star, Marilyn and Natasha that

combined good tolerance of drought stress with a high degree of resistance to scab.


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Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. The trials were

planted in mid-May or early June and harvested in late August or mid-September. In trials conducted

from 2010-2015 this combination of planting and harvest dates resulted in plots harvested at 80, 90,

105 and 120 days after planting. In all years, each treatment was replicated three times. In the 2015

trial, grade out to scab was also evaluated at the 120 day harvest (Table 2015-9) – as this was the first

time that this disease problem has reached damaging levels under irrigated production on this test

site.

Results

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Irrigated Reds (2012)Norland Peregrine

Modoc Sangre

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Irrigated Reds (2013)Norland Peregrine Modoc

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Days after Planting

Irrigated Reds (2011)Norland Peregrine Modoc


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Red skinned cultivars - In trials conducted in 2010-

2015 Norland had a clear yield advantage over all of

the other lines tested at the early harvests (80 and 90

DAP), while the other cultivars produced higher

yields at the later harvests. Peregrine, Modoc and

AR2103 all produced more tubers per plant than

Norland. This reduced the average tuber size – which

was beneficial in situations where the cultivars were

allowed to grow well into the fall. By contrast – if

the standard cultivars Norland and Pontiac are allowed

to grow into September they tend to produce

excessively large tubers which are prone to physical

defects such as growth cracks and hollow heart.

Fig. 2015-2. Yields of red-skinned potato cultivars at different harvest dates in trials conducted

from 2010-2014.

Table 2015-5. Yields of red skinned potatoes at various times after planting (2015)

80 Days 90 Days 105 Days 120 Days Average

T/Ha

Peregrine Red 20.5 37.3 37.2 52.0 36.8

CVXXXX 30.3 35.1 45.6 53.9 41.2

Modoc 32.4 40.1 46.0 54.4 43.2

Norland 45.6 47.7 46.3 50.8 47.6

Pontiac 35.0 49.7 57.3 63.2 51.3

Sangre 20.9 35.5 33.0 51.0 35.1

Average 30.8 40.9 44.2 54.2 42.4

Russets – the russet processing type potatoes tend to be slow growing and late maturing – as is

reflected by their yield profile over time (Table 2015-3). The yield difference between the 80 and

120 day harvests for the russet lines is much greater than is typically seen for the earlier maturing

red-skinned table potato cultivars. The only russet that showed any significant early yields in any of

the trials was Russet Norkotah – it is an early maturing table-type potato with limited potential for

use in processing. Russet Burbank, which is the industry standard for processing was not included in

the 2015 due to problems with seed quality. Russet Burbank had performed poorly in 2010 and

2011, but it was one of the highest yielding cultivars in the trials conducted from 2012 through 2014,

especially at the later harvest dates (Fig. 2015-3). Kennebec which is another standard processing

variety produced large yields at all harvest dates in the 2015 trial – however as noted in Tables 2015-

1 and 2105-4, it is extremely sensitive to scab. Almost all of the Kennebec tubers would have failed

to meet grade standards for scab in both time of planting*time of harvest trials conducted in 2015.

In trials conducted in 2014 and 2015, the new cultivar Ludmilla appeared to have only moderate

yield potential at any of the harvest dates tested. Clearwater which was tested in 2012 and again in

2015 was very late maturing, producing exceptionally low yields unless it was given a full 120 day

development period.

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Irrigated Reds 2014

Norland Peregrine Modoc


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Irrigated Russets (2011)

Premiere Norkotah Burbank Shepody

Alpine Blazer Pacific

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Irrigated Russets (2014)Goldrush Ludmilla

Burbank Norkotah

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Irrigated Russets (2013)Classic Clearwater

Burbank Norkotah

Fig. 2015-3. Yields of russet-type potato cultivars at different harvest dates in trials conducted

from 2010 through 2014.

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Irrigated Russets (2012)Alpine Blazer Classic

Clearwater Burbank Norkotah


14

Table 2015-6. Yields of russet skinned potatoes at various times after planting (2015)


T/Ha

Clearwater 10.5 26.3 32.0 53.8 30.6

Ludmilla 21.3 39.6 37.4 51.1 37.4

Goldrush 25.2 27.9 35.3 51.0 34.9

Kennebec 31.6 49.9 52.3 60.0 48.4

Shepody 27.4 38.0 41.1 48.0 38.6

Russet Norkotah 33.6 36.3 43.3 46.0 39.9

Average 24.9 36.3 40.2 51.7 38.3

Yellow fleshed cultivars – in all years of testing and at all harvest dates, yields of Yukon Gold –

which is presently the industry standard for yellow fleshed potatoes – lagged behind almost all of the

new lines tested at all harvest dates. Yields of Yukon Gold were further reduced due to grade out to

scab – as it appears susceptible to this disease (Table 2015-4). In the 2014 trial, yields of Yukon

Gold were also reduced by Late Blight – and again Yukon Gold appeared to be more susceptible to

this disease than any of the cultivars tested. In all 5 years of testing, the cv. Milva produced excellent

yields, especially at the later harvest dates. Chopin, 401-1 and Miss A. produced exceptionally high

yields at all harvest dates in the 2015 trial. However, all three of these cultivars are highly

susceptible to common scab and grade out to this disease would have severely reduced their

marketable yields. In the 2013 and 2014 trials, the new cultivars Juwel and Toscana showed good

yield potential, especially at the later harvests. In the only year it was tested, the red-skinned yellow

fleshed cv. Belvedere also showed good yield potential at the later harvests. Three “fingerling ”

potato cultivars were tested in 2015 – Natasha, Marilyn and Coquine. Natasha has bright yellow skin

and flesh and appears to be quite resistant to scab – but its yields lagged behind the other yellow

fleshed cultivars included in this trial. Coquine has more of an elongated shape. It is prone to

skinning at the early harvests but if given a full 120 day growing season it produces acceptable yields

of small, relatively scab free tubers.


15

80 Days 90 Days 105 Days 120 Days

Aladdin 39 44 56 61

Annabelle 38 43 54 58

Chopin 46 53 64 64

Jewel 50 53 61 72

Milva 52 54 66 68

Rosara 40 38 54 55

Toscana 40 55 68 74

Yukon Gold 43 37 51 55

Yellow Star 40 48 52 61

(t/ha)

Fig. 2015-4. Yields for irrigated yellow-fleshed potatoes in 2010, 2011 and 2012.

Table 2015-7. Yields of yellow fleshed potatoes at various times after planting (2013)

0

10

20

30

40

50

60

70

80 90 105 120

Yiel

d (t

/ha)

Days after Planting

Irrigated Yellows (2012)

Milva Yukon Gem Yukon Gold Toscana


16

Table 2015-8. Yields of yellow fleshed potatoes at various times after planting (2015)


T/Ha

401-1 45.5 45.1 53.9 58.6 50.8

Bintje 26.3 43.5 47.9 55.7 43.4

Campina 31.6 26.4 45.3 54.3 39.4

Chopin 31.3 53.9 58.0 70.2 53.4

Coquine 25.4 27.8 37.7 52.7 35.9

Marilyn 34.2 39.3 43.7 56.6 43.4

Milva 29.0 41.0 47.7 60.2 44.5

Miss Andes 43.5 53.3 60.1 74.8 57.9

Miss Mignonne 28.4 30.4 48.8 57.1 41.2

Natasha 24.5 35.6 46.5 44.4 37.8

Yukon Gold 19.0 36.8 42.7 36.9 33.9

Average 30.5 39.4 48.9 56.5 43.8

Scab levels in the 2015 irrigated trial were much higher than observed in previous irrigated trials at

this site – and in some cases the scab levels under irrigation were even higher than the levels seen in

the nearby dryland trial. This result was unexpected, as irrigation generally suppresses infection of

the tubers by common scab. The scab was non-uniformly distributed across the irrigated plot area

which led to a high degree of rep to rep variability in the scab ratings Grade out to scab was

extremely high in all of the red-skinned cultivars tested under irrigated conditions in 2015 – with

many of the cultivars producing no marketable yields after grade out to excessive scab. As was seen

in the dryland trial, the standard cultivar Norland was the most scab resistant of the red-skinned

cultivars tested. Grade out due to excessive scab in the 2015 irrigated trial was much less common in

the thicker skinned russet varieties than in the thinner skinned red or yellow varieties. A similar

result was seen in the dryland trial. Kennebec was the only russet type potato that had a significant

degree of grade out to scab under irrigation. Of the yellow fleshed cultivars tested under irrigated

conditions, Natasha, and Marilyn showed good levels of scab tolerance – but as seen in previous

trials – Milva was the most scab resistant yellow fleshed cultivar available. Coquine, which had

formed little scab under dryland conditions appeared to be highly scab sensitive under irrigation.

This difference does not make sense and merits further investigation. Once again, Yukon Gold,

which is presently the standard yellow fleshed cultivar grown in Saskatchewan, proved to be

sensitive to scab – producing no marketable tubers when grown in a scab infested soil – even under

irrigated conditions.


17

Table 2015-9. Yields, scab intensity levels and yields after grade out to scab at 120 days after

planting under irrigated conditions in 2015.

Yield (t/ha)

Scab


Reds

AC Peregrine 52.0b 33cd 0b Modoc 54.4b 21de 16.3a

CVXXXX 53.9b 50b 0b Norland 50.8b 17e 20.3a Pontiac 63.2a 73a 0b Sangre 51.0b 39bc 0b

Avg 54.2 38.8 6.1

Russets Ludmilla 51.1ab 0c 51.1a

Clearwater 53.8ab 0c 53.8a Goldrush 51.0ab 0c 51.0a Kennebec 60.0a 37a 3.0c

Russet Norkotah 46.0b 13a 27.6b Shepody 48.0b - -

Avg 51.7 10.0 37.3

Yellows 401-1 58.6ab 76a 0e Bintje 55.7abc 65ab 0e

Campina 54.3abc 18d 27.1bc

Chopin 70.2a 55b 0e

Coquine 52.7bc 75a 0e

Marilyn 56.6abc 13d 22.6c

Milva 60.2a 8d 48.1a Miss Andes 64.8ab 71a 0e

Miss Mignonne 57.1abc 29c 11.2d Natasha 44.4cd 10d 33.3b

Yukon Gold 36.9d 74a 0e

Avg 54.0 47.5 11.9 For each skin colour type, values within columns followed by the same letter are not significantly different (P=0.05)


Tubers graded out if >5% of the tuber surface area was affected by scab

Specific gravities – are used as an indicator of the dry matter content of the potato. High dry matter

content potatoes tend to have a mealy texture, making them better suited to baking than boiling.

High specific gravity potatoes are required by manufacturers of chipped or fried potatoes, as a high

specific gravity potato tends to result in a crisp final product.


18

A comparison of the specific gravities seen for the various cultivars at the most mature date in each

season (120 day harvest) is presented in Table 2015-10. Specific gravities are more important for the

processing type potatoes than for cultivars bred for use as table stock. As expected, specific gravities

of all cultivars increased the longer the crop was allowed to grow. Again as expected, specific

gravities of the processing type russet cultivars were higher than the table-type red or yellow

cultivars. Although Clearwater had low yields at all harvest dates, its specific gravities were

consistently high which may explain the popularity of this cultivar with processors. Significant year

to year variation was observed for the specific gravities achieved by 120 days after planting (Table

2015-7). This reflects differences in the suitability of the growing season for potato production – in

general, more favorable conditions result in higher specific gravities.

Table 2015-10. Specific gravity of new potato cultivars at 120 days after planting in the 2012

2014 growing seasons.

2012 2013 2014

Reds

AC Peregrine 1.081 1.089 1.082

Norland 1.076 1.078 1.068

Modoc 1.076 1.074 1.065

Russets

Alpine 1.087

Blazer 1.086

Classic 1.085 1.093

Clearwater 1.093 1.103

R. Burbank 1.089 1.097 1.089

R. Norkotah 1.086 1.079 1.078

Yellows

Aladdin 1.086

Annabelle 1.078

Chopin 1.078 1.071

Juwel 1.080 1.074

Milva 1.084 1.087 1.078

Rosara 1.084

Toscana 1.075 1.067 1.076

Yukon Gold 1.089 1.090 1.076

Yellow Star 1.082 1.072

Avg 1.083 1.084 1.075

Summary of Time of Planting and Harvest Trials

The results of the time of planting and harvest date studies indicate the importance of maximizing the

duration of the effective growing season for growers in Saskatchewan. Yields and processing quality

(specific gravities) of most new and industry standard cultivars tested increased progressively with

duration in the field through to 120 days. A 120 day season represents the effective maximum

available to potato growers in Saskatchewan - as earlier plantings or later harvests run into excessive

risk of frost damage. By contrast, some growers opt for a very short duration growing season. In the


19

seed industry this is used to minimize the risk of virus infection, whereas in the table sector, growers

may opt for an early harvest to catch a high value market opportunity or to keep the size of their

tubers within the optimum range desired in the marketplace. The results clearly illustrate the

magnitude of yield sacrifice associated with an early harvest. The relative amount of yield loss

associated with an early harvest was greater for late maturing cultivars like Modoc, Toscana, Juwel,

Belvedere, Russet Burbank, Classic, Ludmilla and Clearwater than for earlier cultivars like Russet

Norkotah or Norland. This suggests that growers should use caution when growing these slower

maturing cultivars, as a slow start to the season, an unusually cool summer or an early fall could

severely depress yields. In all cases the increase in yields with time in the field was strictly a

function on an increase in average tuber size, rather than any increase in tubers produced.

As potatoes mature their specific gravity (dry matter content) increases and their reducing sugar

content declines. These changes result in potatoes that process well. The specific gravity data

generated in this project clearly indicates the importance of growing suitable cultivars and extending

the growing season for as long as possible in order to maximize specific gravities.


20

N-Fertility Trials At present, N fertility recommendations for potatoes in Saskatchewan range from 150 # N/a

(dryland) to 190 # N/a (irrigated). The objective of this trial was to determine optimum N-fertility

rates under irrigation for a range of new potato cultivars. The soil-N treatments (total of 50, 100,

150, 200 or 250 # N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the

residual soil N (ca. 50 # N/a). The N-treatments were laid out in an incremental design with two

replicates.

Results

N Fertility responses for cv. Blazer, Alpine, Milva, Classic and Clearwater have been presented in

previous reports.

Modoc is a red-skinned white flesh table potato similar in appearance to the standard Norland. The

yield response of Modoc to increasing rates of applied N was very flat in 2013, but increased until

150 kg N/ha was available in the 2014 trial.

Juwel – is a high yielding, late maturing yellow fleshed

cultivar. In the 2014 trial, yields of Juwel increased until

200 kg N/ha was available.

0

10

20

30

40

50

60

70

50 100 150 200 250

Yie

ld (

t/h

a)

Total Soil N (#/a)

Modoc - 2013

Medium Small

0

10

20

30

40

50

60

70

50 100 150 200 250

Yie

ld (

t/h

a)

Total Soil N (#/a)

Juwel - 2014

Medium Small

0

10

20

30

40

50

60

70

50 100 150 200 250

Yie

ld (

t/h

a)

Total Soil N (#/a)

Modoc - 2014

Medium Small


21

Yellow Star – is a late maturing yellow fleshed cultivar

with limited yield potential under the relatively short

growing season available in SK. In the 2014 trial, yields

of Yellow Star increased until 150 kg N/ha was

available.

Ludmilla – is a russet skinned cultivar which processes well directly out of cold storage. Yield

potential of Ludmilla is only moderate under the relatively short growing season available in SK. In

the 2014 trial, yields of Ludmilla increased until 150 kg N/ha was available and then declined quite

drastically if the crop was supplied with higher levels of N. In the 2015 trial, yields of Ludmilla

increased through to the highest N fertility level tested (250 #/a). The maximum yields obtained in

2015 were very similar to those obtained in 2014, but the 2015 crop required far more fertilizer to

obtain those yields.

Coquine – is a yellow fleshed cultivar that

produces large numbers of small, elongated tubers.

In its first year of testing in 2015 the overall yield

potential of Coquine appeared to be moderate.

Peak yields of Coquine were obtained with

relatively low inputs of N (100 #/a total N) – this is

substantially less N than the requirement of most

popular cultivars. The proportion of the tubers

that graded into the “small” size category was

0

10

20

30

40

50

50 100 150 200 250

Yiel

d (t

/ha)

Total Soil N (#/a)

Yellow Star - 2014

Medium Small

0

10

20

30

40

50

50 100 150 200 250

Yiel

d (t

/ha)

Total Soil N (#/a)

Ludmilla - 2014

Medium Small

Ludmilla - 2015

0

10

20

30

40

50

50 100 150 200 250Total Soil N (#/a)

Yie

ld (

t/H

a)

Medium Small

Coquine - 2015

0

10

20

30

40

50

60

50 100 150 200 250Total Soil N (#/a)

Yie

ld (

t/h

a)

Medium Small


22

consistently high across all N fertility treatments in the 2015 trial of Coquine.

CVXXXX – is a new red-skinned, white flesh

cultivar with a moderate yield potential. In its first

year of testing in 2015, yields of CVXXXX

increased to a peak at 200 #/a total N.

Conclusion - The N fertility responses;

a) varied from cultivar to cultivar,

b) were not consistent from year to year and

c) were quite limited - in that the lowest rate of total N (50 #/a) typically produced yields that

were within 10% of the highest yielding treatments.

The inconsistency of the N fertility responses from year to year is likely driven by differences in the

relative suitability of the growing season for potato growth. In poor growing seasons, yield

responses to fertility treatments may be small, as the availability of N is not limiting growth.

While supra-optimal rates of applied N seldom had any significant negative impact on yields they

may have had a negative impact on crop quality. The heavy canopy resulting from the application of

surplus N may promote development of Late blight and it also interferes with top-killing and harvest.

The observation that yields within 10% of the site maximum were consistently obtained without

adding any N fertilizer – but instead relying solely on the residual soil N of ca. 50 #/a - was

unexpected. Potatoes are regarded as having a high N requirement, with vegetative growth showing

a strong response to N fertilizer applications. However, tuber yields can be influenced by many

factors and consequently the linkage between soil N availability and yield is less clear cut.

Defoliation due to late blight may have limited the N fertilizer response in the 2010 trial – however,

yields in the other years of testing were quite high, suggesting that there were no major yield limiting

factors at play. The blight resistant cultivar Milva produced exceptionally yields in all 3 years of

testing – and in all years it showed almost no yield response to soil N beyond the baseline of 50#/a.

This suggests that either Milva has exceptionally high N use efficiency or that the soil at the test site

has exceptionally high levels of N present in a form not apparent in standard soil tests. Zebarth et al

(2004 - Can. J. Plant Sci. 84: 845-854) showed that a combination of relatively modest residual soil

NO3, plus the N made available through the growing season via mineralization of soil organic matter

could provide sufficient N fertility to produce yields within 15% of the maximum achieved using up

to 175 #/a of applied N.

At present, the economics of potato production dictate that growers should strive to maximize yields,

even if it involves the application of very high rates of N fertilizer. As the cost of N increases and/or

concerns increase regarding the environmental impact of over-application of fertilizers, the data

generated in this study suggest growers of potatoes in SK can cut their N applications substantially

without a significant yield penalty - and this management decision may actually increase crop

quality.

CVXXXXX

0

10

20

30

40

50

60

50 100 150 200 250Total Soil N (#/a)

Yie

ld (

t/h

a)

Medium Small


23

Spacing trial

As in previous years, the effect of in-row spacing on yields was fairly consistent across the cultivars

evaluated in 2015. The closer the in-row spacing, the higher the total yields - with a less obvious

spacing effect on yields at the wider row spacings (Figs. 2015-5, 6, 7, 8, 9 and 10). The degree of

yield difference between the spacings tested was smaller in 2015 than in most other years. In all

years there was a small but consistent tendency for the average tuber size to decrease along with the

in-row spacing – but the effect was not significant in most cases.

0

20

40

60

80

Alpine Blazer GemStar Milva Opearle

Yie

ld (

t/h

a)

6" 10" 14"

0

20

40

60

80

Alpine Blazer Milva Modoc

Yie

ld (

t/h

a)

6" 10" 14"

Fig. 2015-6. Impact of in-row spacing on tuber yields in 2011.



24

0

20

40

60

80

Alpine Blazer Milva Modoc

Yie

ld (

t/h

a)

6" 10" 14"

Conclusion - The results of the spacing trials conducted from 2010-2015 illustrate the

responsiveness of potato to manipulation of plant populations. If the objective is to maximize yields,

a close in-row spacing is desirable, as long as reaching a certain minimum tuber size is not a

significant issue. In seed production or when growing for the “creamer” or “baby” potato markets,






0

20

40

60

80

CVXXXX Ludmilla Conquine Miss Andes Miss Mignonne

Yie

ld (

t/h

a)

6" 10" 14"

0

20

40

60

80

Belvedere Juwel Yellow Star Modoc

Yie

ld (

t/h

a)

6" 10" 14"


25

close in-row spacing would produce high yields and a highly desirable small average tuber size

distribution. The table and processing sectors are looking for a larger size profile - and therefore

slightly wider in-row spacing would likely be more desirable. The data suggests that this larger

sizing can usually be achieved without an excessive compromise in yield potential. It is noteworthy

that yields were increasing with plant population through to the closest spacing used ie; 6". This

raises two questions;

a) Would the trend continue for an even closer spacing?

We suspect that the yield profile would tend to plateau - with the cost benefit ratio depending

on the relative cost of seed versus the harvested crop. For some cultivars like O’Pearle and

Peregrine, the yield profile at 6" was already quite small. There is a substantial price penalty

in table markets if the tuber size falls below “A” size (1 3/4" or 55 mm diam). If however, the

tuber size falls all the way to a “Creamer” size (1" or 25 mm) these tubers command a price

premium as “Baby” potatoes. The fact that yields of Creamer sized potatoes for most

cultivars tested was still increasing as in-row spacing narrowed to 6” suggests that there may

be advantages of even closer in-row spacing if the objective is to maximize yields of small

tubers.

b) Would a commercial grower expect to see the same responses?

The yields obtained in this trial were in excess of those obtained in typical commercial fields

in SK. This may reflect efforts to manage all inputs so as to minimize crop stress or

competition for resources. These management practices would have allowed the crop to

express its full yield potential - even when there were very large numbers of plants competing

for resources. However, the cost and cost efficiency of this type of management regime was

not considered. If a grower cannot or does not provide the same stress-free production

environment, this will lead to competition between plants within the row - with a

corresponding reduction in yield potential. This loss of yields will be greatest in situations

where a high plant population tends to exacerbate competition effects. Growers will need to

tailor their plant populations to match their ability to manage the crop while also factoring in

costs of production and anticipated yields and economic returns.


26

Consumer Panels

Yellow fleshed potatoes are becoming increasingly popular in Canada – in part as a function of their

“novelty” value, but also because of their higher Vitamin A content and their perceived superior

flavor. For many years Yukon Gold has been the standard yellow fleshed table potato across North

America. However, Yukon Gold has some significant production limitations – especially its

tendency to go oversize and as demonstrated in this project it is sensitive to drought stress and prone

to common scab. Several of the new yellow fleshed cultivars tested in this project – including Milva,

Yellow Star, Natasha and Toscana have agronomic characteristics that are clearly superior to Yukon

Gold. However, before growers shift to a new cultivar with superior agronomic qualities they must

be sure that the cultivar is also acceptable to their customers – who care about issues such as tuber

appearance and flavor. The objective of this aspect of the project was to assess consumer

reaction to the new yellow fleshed potato cultivars available to growers in Saskatchewan.

The potatoes used in the consumer panels were all grown, harvested, and graded as previously

described. The potatoes were evaluated after 3 months of cold storage (5oC and 50% R.H.). Four

randomly selected tubers of each cultivar were pealed then boiled in unsalted water for 20 minutes

until cooked, then cooled and cubed prior to the taste assessment. Panelists (10 in 2011, 13 in 2012,

20 in 2013,18 in 2014 and 2015) were asked to rank each cultivar from best (rank of 1) to worst for

how “yellow” the flesh color was and for the flavor of the cooked tubers. Panelists were not

informed as to the identity of the cultivars they were evaluating.

Results

Yellow Flesh Color

mean rank and (range)

2011 2012 2013 2014 2015

Milva 1.3 (1-3) 2.5 (1-4) 2.6 (1-6) 2.2 (1-6) 2.1 (1-4)

Toscana 2.2 (1-4) 5.1 (2-7) 2.2 (1-5)

Y. Gem 2.1 (1-3) 2.9 (1-4)

Y. Gold 2.6 (1.3) 2.4 (1-4) 6.2 (4-8) 5.8 (5-7) 4.4 (2-6)

Rosara 4.2 (2-5)

Yellow Star 5.3 (3-8) 3.9 (1-5)

Aladdin 7.3 (2-9)

Juwel 3.2 (1-5) 5.2 (4-7)

Chopin 3.6 (2-6) 6.7 (5-7) 5.7 (3-7)

Annabelle 1.3 (1-3)

Belvedere 2.7 (1-6)

Miss Andes 5.3 (3-7)

Miss

Mignonne

2.9 (1-4)

Campina 4.9 (3-6)

Natasha 2.5 (2-4)

Bintje 5.5 (3-7)

Marilyn 3.4 (2-5)

401-1 4.7 (3-6) Low rank values indicate darker yellow color.


27

Flavor

mean rank and (range)

2011 2012 2013 2014 2015

Milva 1.6 (1-3) 1.6 (1-2) 3.6 (1-9) 3.8 (1-8) 3.2 (1-7)

Toscana 2.8 (1-4) 1.4 (1-3) 3.4 (1-6)

Y. Gem 2.4 (1-3) 2.5 (1-4)

Y. Gold 2.0 (1.3) 3.1 (1-4) 4.2 (1-9) 3.5 (2-7) 4.6 (1-7)

Rosara 5.4 (2-8)

Yellow Star 3.7 (1-7) 5.2 (1-8)

Aladdin 5.4 (2-9)

Juwel 3.8 (1-9) 4.1 (2-7)

Chopin 3.7 (2-6) 3.4 (1-7) 3.8 (1-6)

Annabelle 3.6 (1-5)

Belvedere 2.4 (1-6)

Miss Andes 3.0 (2-5)

Miss

Mignonne

3.1 (2-6)

Campina 2.4 (1-5)

Natasha 5.3 (4-6)

Bintje 4.0 (1-7)

Marilyn 5.2 (4-7)

401-1 3.5 (2-5) Low rank values indicate greater consumer preference.

The results clearly demonstrate the subjectivity of panel results. For both color and flavor many

cultivars were rated the best by at least one panellist and the worst by another.

Over the 4 years of testing, Milva and Toscana were consistently rated as having the darkest yellow

flesh. Milva received the highest flavor ranking in 2011 and 2012, Toscana was the top rated variety

in 2013, Belvedere was rated as best tasting in the 2014 trial and Campina was best in 2015.

It is noteworthy that Yukon Gold (see highlighted above), which is presently the industry standard

for yellow fleshed varieties, was not highly rated in any of the trials for either flesh color or flavor.


28

Late Blight Sensitivity

Late Blight was observed in the test plot area in late August of 2014. This provided an opportunity

to assess the relative Late Blight sensitivity of the test varieties – both to foliar damage by this

pathogen and also to tuber rot.

Assessment of the relative susceptibility of the foliage to infection by L. blight was evaluated 7 days

after the L. Blight was initially spotted in the field. During the intervening period of time the field

had been sprayed twice with fungicides in an effort to slow development of this disease – but disease

development had nonetheless occurred. Each row of each cultivar was visually rated for infection of

the foliage by L. blight using a scale of 0 – 5 with 0 = no blight observed, 1= lesions present on 1%

of the leaves, 2=10% of the leaves, 3 = 25% of the leaves, 4=50% of the leaves and 5= all leaves

affected.

The cultivars Modoc and Norland showed the most

damage However, as Norland is typically already

senescing by this point in the growing season, some of the

observed leaf damage may not have been due to blight.

Milva showed the least sensitivity to foliar infection by the

L. Blight pathogen. Milva’s resistance to blight has been

observed in previous trials.

This trial also provided an opportunity to assess the relative

degree of sensitivity of the various lines to tuber infection

and subsequent tuber rot by the blight pathogen. Although

the foliage of Shepody showed only moderate sensitivity to

infection by the blight, tuber infection and subsequent

tuber rot in this cultivar was far more prevalent than in any

of the other cultivars tested. Significant grade out to blight

was also seen in Yukon Gold, with lesser levels of decay in

Norland and AC Peregrine. In all the other lines tested in

2014 there were very few tubers affected by the disease.

Late Blight

Damage Rating

(0-5) AC Peregrine 2.3 Belvedere 1.7 Chopin 2.3 Goldrush 2.0 Juwel 2.7 Kennebec 1.7 Ludmilla 1.7 Milva 0.7 Modoc 4.0 Norland 3.7 Russet Burbank 1.0 Russet Norkotah 2.0 Shepody 2.3 Toscana 2.0 Yukon Gold 2.7 Yellow Star 1.3

Rating of 0=no damage, 5= 100% of leaves damaged


29

Review of the agronomic responses of the new cultivars tested in 2012-2015;

Milva

Milva is a potential alternative to Yukon Gold as a smooth

skinned yellow fleshed table potato. Milva demonstrated

exceptional yield potential, even in early harvests. Under

rainfed production, yields of Milva were consistently higher

than any other yellow fleshed cultivar tested. Milva also

appears to require relatively little fertilizer N to achieve these

very high yields. Milva’s tuber size distribution is more

uniform than Yukon Gold and it also shows less tendency to

oversize. Milva is exceptionally tolerant of Late Blight and

also has far fewer problems with common scab than Yukon

Gold. In consumer panels the color and flavour of Milva was

consistently preferred over Yukon Gold. The only significant limitation of Milva may be that

its tubers are tear-drop shaped - and this shape is not familiar in the North American

marketplace.

Blazer, Alpine, Clearwater and Classic

All of these newly released processing type russet potatoes are showing promise in North

Western USA – but there was some concern as to where the growing season in Saskatchewan

would be long enough to allow these varieties to fully mature. This will be important as

Saskatchewan seed potato growers begin to plant these varieties in order to meet the seed

potato needs of their customers in the USA. Based on the time of planting and harvest trials,

the 120 day growing season available in Saskatchewan is not sufficient to allow Alpine,

Blazer, Classic and Clearwater to reach full size and maturity. Classic plants produce a small

number of tubers/plant – and these tubers grow to exceptional size. This trait may be

beneficial when selling to processors, but will be problematic when attempting to grow this

potato for seed. Alpine showed superior processing potential, especially during early

harvests. All these russet type potatoes showed high levels of tolerance of common scab. In

the 2012 trial cv. Blazer showed some sensitivity to Late Blight. In the 2013 trial, Clearwater

showed outstanding processing quality.

Modoc

This newly released red-skinned table cultivar showed some

promise as it produced yields that were comparable to the

industry standard reds (Norland and Peregrine). Modoc has

superior tuber colour and appearance than Norland,

especially after significant periods of cold storage. Modoc is

more prone to damage by common scab and Late Blight than

is Norland. Yields of Modoc are also quite sensitive to

moisture stress. The N fertility requirements of Modoc are

moderate (100-150 kg a/ha).


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Juwel

Juwel is a high yielding, late maturing yellow fleshed

cultivar that produces larger oval tubers. Juwel is

moderately resistant to common scab and late blight. In

consumer panels Juwel was not rated highly for either its

color or flavor.

Chopin

Chopin is a late maturing yellow fleshed potato. Chopin

was not outstanding for any of the yield or consumer quality

characteristics tested in this project. Chopin is also very

sensitive to common scab.

Yellow Star

Is a late maturing yellow fleshed potato with which produces large numbers of small oval

shaped tubers. The skin of Yellow Star is smooth and bright yellow but its flesh color was

rated as only moderately yellow. Its flavor ranked near the middle of the yellow-fleshed

cultivars tested. Yields of Yellow Star were lower than most of the other yellow-fleshed

varieties tested at all harvest dates. Yellow Star appears to be quite resistant to foliar

infection by Late Blight and it is outstanding for its resistance to tuber damage by common

scab.

Toscana

Toscana produces good yields of medium sized

uniform oval shaped tubers. Its flesh color was

rated as very dark yellow and its flavor was rated

highly by the taste panels. Toscana showed

moderate resistance to common scab and late

blight.


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Ludmilla

Ludmilla is a processing type potato with light

yellow flesh. Its heavy russet skin protects

Ludmilla from scab and skinning at harvest.

The yield potential for Ludmilla is only average

– but it appears to be better suited for processing,

especially out of cold storage, than other russet

type potatoes.


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new potato cultivars - university of...

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